German Patent Application No. 34 00 711 (corresponding to U.S. Pat. No. 4,638,782) describes a process and a device for open and/or closed-loop control of an actuator, in particular for influencing fuel delivery in an internal combustion engine. A system deviation is determined from a setpoint and an actual value. From the system deviation, a controller defines a manipulated variable to be supplied to an actuator. At high engine speeds, control with this device is preferably performed using a controller with PI action. In other operating states (i.e., at low engine speeds) the actuator is only controlled using open-loop control.
In order for such controllers to satisfy the high requirements, in particular regarding dynamics, complex control circuit structures are needed. One possible way to meet those requirements is a use of variable-structure controllers which, under certain conditions, can be toggled between different controller structures. Thus, the controller may be able to, switch back and forth between a PI controller and a proportional (or a pure) open-circuit controller.
The switching action is problematic in the prior art. When switching from one controller structure to another controller structure, undesirable transient phenomena often occur. If a proportional control with a high gain used as a large-signal controller is switched to a PI controller used as a small-signal controller, I component must be suitably preset to avoid undesirable controller characteristics, i.e., oscillations.